Hermetically sealed cell and sealing body

ABSTRACT

The object of the present invention is to provide a closed battery capable of rapidly releasing the internal pressure thereof and at the same time disconnecting the current to effectively prevent itself from temperature rising and explosion so that it may assure the safety and reliability thereof, when the internal pressure is elevated due to short circuit, overcharge, reverse charge, or the like in such a completely closed battery. The formation of a valve element  5  whose center is eccentric to the center of a metal substrate  1  produces a slit  3  having a large width portion around the circumference of a valve element  5 . When the internal pressure of a battery is elevated, the valve element  5  is smoothly raised up together with a metal foil  2  from the bending fulcrum portion  4  to thereby cut a lead wire  6  or permit a braze portion  8  to detach from the lead wire  6 , thus reliably disconnecting the current. Then, the metal foil is allowed to burst stably and accurately at a prescribed pressure to thereby form a valve opening portion  7  so that the internal gas of the battery can be discharged. Thus, the battery can previously be prevented from exploding.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the national stage under 35 U.S.C. 371 ofPCT/JP98/02054, filed May 8, 1998.

DETAILED DESCRIPTION OF THE INVENTION

1. Field of the Invention

The present invention relates to a closed battery capable of bursting ata prescribed pressure, especially at a low pressure, to rapidly releasethe internal pressure and at the same time to break a current, when thetemperature or internal pressure of the battery is elevated, and to aclosing member for use in the closed battery.

2. Prior Art

Recently, with increasing requirement of electronic devices that aremade much smaller in size and light weight and have enhancedperformance, the use of non-aqueous batteries with high energy densityhas become popular. Batteries which use an alkaline metal such aslithium, sodium, or potassium as an active material of negativeelectrode thereof employ battery containers of completely closedstructure because the alkaline metal easily acts with water.

Such a completely closed battery has a merit of storability, but inreverse, its high sealability sometimes causes rupture of the batteryitself due to the abnormally elevated internal pressure thereof in caseswhere the battery is exposed to high temperature, or a short circuit isformed inside or outside of the battery to cause a large flow of thecurrent, or a hydrogen gas is generated in the battery due to watercontamination penetrated in the manufacturing process thereof. In such acase, the device that accommodates such a rupturing battery will bebroken and moreover, there may be a danger of the broken device andbattery harming the user. Accordingly, there should be a request forsome pressure releasing mechanism before the internal pressure of thebattery is increased to such a high extent.

So far, several methods for releasing the internal pressure of a batteryhave been proposed and some of them have been used in practice. Forinstance, Japanese laid-open publication HEI 2-304861 discloses a safetyvalve for a battery, which comprises a valve chest provided at a part ofa container of the battery and having a valve through hole to becommunicated with the inside of the battery and an outlet to becommunicated with the outside, the valve chest comprising a valve memberat least whose surface opposed to the valve through hole is made ofrubber, and an elastic member for pushing the above mentioned rubbersurface of the valve member to the valve through hole. This safety valveholds the sealability of the battery by closing the valve through holewith the rubber-made valve member, and prevents the internal pressure ofbattery from rising in excess of a prescribed pressure by permitting thevalve through hole to be opened when the internal pressure rises to thepressure presribed for the elastic member.

Such a conventional safety valve has been widely used in Ni-Cd typebatteries. However, it has not yet been used in the non-aqueousbatteries which employ alkaline metals as the active material of thenegative electrode, since even if the elastic member presses the valvemember to the valve through hole to thereby close the battery, it isimpossible to obtain such a high sealability as required for thenon-aqueous batteries.

One of the methods for releasing the internal pressure of a batterywhich requires high sealability is disclosed in Japanese laid-openpublication SHO 63-285859. In this method, a container of the battery isprovided with a thinned portion at a part of its wall. This thinnedportion is formed by cold rolling a sheet of the vessel using a pressdevice until the thickness of the rolled portion of the sheet becomeshalf of the initial thickness thereof. Thus, the battery is providedwith good sealability with regard to this thinned wall portion becauseit is only transformed from a part of the continuous wall of thecontainer.

Another pressure releasing mechanism of this type is disclosed inJapanese laid-open publication HEI-6-215760. This releasing mechanismcomprises a valve diaphragm fitted in an open end of the cylindricalcontainer of a battery having a bottom and disposed above the electrodeelement of the battery, and a lead for breaking current disposed abovethe valve diaphragm. In this structure, when the internal pressure ofthe battery is elevated, the valve diaphragm is expanded to rupture thelead for breaking current to break the current.

PROBLEM TO BE SOLVED BY THE INVENTION

According to the method as disclosed in Japanese laid-open publicationSHO-63-285859, it is necessary to obtain a thinned wall portion of thecontainer so that the thinned portion can be ruptured at a relaively lowpressure. However, when the wall portion is made too thinned, there maybe formed fine or minute cracks during press-forming, thus impairing thesealability of the battery container.

Further, when metals are processed by cold working, they inevitably workharden. However, the hardening of the metals does not always takes placeuniformly, and therefore, there arises a problem that the operatingpressure for such pressure releasing mechanism cannot regularly becontrolled. There has been further proposed a half-etching method formaking thinner a part of the wall of a battery container, it isextremely difficult to control the remaining thickness of the thinnedportion after etching, and also difficult to obtain a good yield.Another problem is that the half-etched portion cannot be free from theformation of pinholes, and therefore, all the products need to beinspected.

On the other hand, according to the method as disclosed in Japaneselaid-open publication HEI-6-215760, it is necessary to accuratelycontrol the depth of a cut portion formed in the lead. This is a severeproblem in view of its working process. Another problem is that thecurrent is not reliably broken at a prescribed pressure.

With a view to solving the conventional drawbacks as mentioned above, itis an object of the present invention to provide a closed batteryincorporating a valve chip which can be stably and accurately burst at aprescribed pressure, especially at a low pressure, so as to release theinternal pressure thereof and can be manufactured easily, and provide aclosing member for use in said closed battery.

MEANS FOR SOLVING THE PROBLEM

The present invention provides a closed battery which comprises: anelectrode element consisting of a positive electrode, a negativeelectrode, and a separator; an electrolyte; a battery containeraccommodating said electrode element together with said electrolyte; anda closing member fited in the inner periphery of an open end portion ofsaid battery container to close the open end portion of the batterycontainer, wherein said closing member consists of a metal substrate, avalve element which is provided with a slit in said metal substrate soas to serve as a releasing chip such that when the internal pressure ofthe battery is elevated, the valve element is bent from a bendingfulcrum so as to provide the metal substrate with an opening portion forreleasing the internal pressure, and a metal foil which is adhered tothe inner surface of the metal substrate, wherein said valve element isdefined by a slit having a width, in other words, the slit is formedbetween the circumference of the valve element and the metal substrate,and the center of the valve element is eccentric to the center of themetal substrate. The present invention also provides a closing memberfor use in said closed battery.

According to the present invention, when the internal pressure of abattery is elevated due to short circuit, overcharge, reverse charge, orthe like, a valve chip consisting of a metal substrate in which a valveelement is provided for releasing the internal pressure of the battery,and a metal foil which has a uniform and accurate thickness and is laidover the metal substrate so as to close a through hole which is usuallyclosed with the valve element, operates to transform itself and push andraise the valve element. At this time, since the valve element is formedeccentrically to the metal substrate, the slit between them is allowedto have a wide width, which facilitates the operation of the valve chipV. When the valve chip is electrically disconnected and the internalpressure reaches to a prescribed pressure, the valve element is smoothlyraised up thanks to the formation of such a wide slit, and the metalfoil bursts stably and accurately to discharge the internal gas of thebattery so that an abrupt rising of the internal temperature orexplosion of the battery can previously be prevented.

PREFERRED EMBODIMENT

The present invention is now explained in conjunction with preferredembodiments and examples referring to the drawings. FIG. 1 is a verticalsection view showing an upper part of a completely closed battery of thepresent invention. FIG. 2 is a plane view showing a valve chip of theclosed battery of the present invention. FIG. 3 is a vertical sectionview showing the above mentioned valve chip. FIG. 4 and FIG. 5 areexplanatory views showing operating manners of the valve chip in case ofabnormality. FIG. 6 is a plane view showing another embodiment of thevalve chip.

In FIG. 1, a cylindrical battery container 30 having a bottom, whichserves as a negative electrode terminal, accommodates an electrodeelement 32 together with an electrolyte which are isolated from theoutside. The electrode element 32 is constituted of a coiled laminatewhich comprises a positive electrode 32 a, a separator 32 b, and anegative electrode 32 c disposed opposite to the positive electrode 32 avia the separator 32 b.

A closing cap 33 having through holes 0 and 0 which serves as aexplosion-preventing mechanism and at the same time as a positiveelectrode terminal is fitted by calking in the upper open end portion ofthe container 30 via an insulating gasket 34. Above the electrodeelement 32, a saucer-like inner cap 37 is disposed and a gas releasehole of a large diameter 35 is provided at the center portion of theinner cap 37.

Between the inner cap 37 and the closing cap 33, a valve chip V whichforms a closing member for enclosing the electrode element and others isprovided. A periphery 36 of the valve chip V is in contact with aperiphery 33 a of the closing cap 33. These peripheries 36 and 33 a arefixed by calking in a circumference 37 a of the inner cap 37 via aninsulating gasket 40.

A lead wire 6 is attached, by an appropriate means, to an inner surfaceof the valve chip V serving as the closing member for closing theupperopen end portion of the battery. The lead wire 6 extends to thepositive electrode 32 a of the electrode element 32.

As shown in FIG. 2 and FIG. 3, the valve chip V is substantiallycircular in a plane view, and is composed of a metal substrate 1 havinga circular form and a metal foil 2 adhered to the inner surface of themetal substrate. As a material of the metal substrate 1, any oneselected from the group including a steel sheet, stainless steel sheet,copper sheet, and aluminum sheet may be used. As a material of the metalfoil 2, any one selected from the group including a steel foil,stainless steel foil, copper foil, aluminum foil, nickel foil, andnickel-iron alloy foil may be used.

A valve element 5 is formed in the metal substrate 1 with the centerthereof eccentric to that of the metal substrate 1 so that a slit 3between the valve element and the metal substrate has a widthpositionally varied such that the slit may obtain a crescentic form. Theslit 3 having such a width penetrates through the metal substrateentirely in its thickness direction. The valve element 5 has a part withno slit formed, which is to be a bending fulcrum portion 4. The slit 3is so formed that a portion of the slit reverse to the bending fulcrumportion with regard to the center of the valve element 5 is providedwith the maximum width of the slit and the width is gradually decreasedfrom this maximum wide portion toward both ends of the slit 3. An innerportion defined by the slit 3 constitutes the valve element 5 which isto operate as a pressure releasing chip for releasing the internalpressure of the battery when the internal pressure is elevated. When thevalve element 5 is raised up from the bending fulcrum portion 4, a valveopening portion 7 will be formed so as to release the internal pressureof the battery. (See FIG. 5.) The lead wire 6 is attached to the metalfoil 2 through a braze portion 8, for instance.

Next, an operating manner of the valve chip in case of abnormality isexplained. Now, a gas decomposed from the electrolyte of a battery isgenerated due to overcharge or the like, which raises the internalpressure of the battery. In this case, since the valve chip V isprovided with the crescent-like slit 3 having a width which ispositionally varied, the valve element 5 is smoothly raised up at arelatively low pressure and at a relatively large angle θ together withthe metal foil 2, from the bending fulcrum portion portion 4, as shownin FIG. 4, to thereby permit the braze portion 8 to detach from the leadwire 6, thus reliably disconnecting the current. Then, a part of themetal foil 2 corresponding to the crescent-like slit 3 having a widthwhich is positionally varied bursts to form the valve opening portion 7so that the internal pressure is released outside. The gas generatedfrom the electrolyte passes through the valve opening portion 7 and isdischarged from the through holes 0 of the closing cap 33. Incidentally,while the valve element 5 is raised up from the metal substrate from thebending fulcrum portion 4, since the center Cl of the valve element iseccentric to the center C2 of the valve opening portion 7, there isproduced a space wide enough to form a large valve opening portion.

The form of the valve element is not necessarily limited to thesubstantially circular form as shown in FIG. 2, but the valve elementmay be one as denoted by 10 in FIG. 6, which is provided with an armportion 4a at the bending fulcrum portion 4. According to thecomposition of the present invention, in a completely closed battery ,thanks to the formation of the slit 3 having a large width portion, whenthe internal pressure of the battery is elevated due to some abnormalitysuch as short circuit, overcharge, or reverse charge, the valve element5 is smoothly raised up together with the metal foil 2 from the bendingfulcrum portion 4, as shown in FIG. 4, to thereby cut the lead wire orpermit the braze portion 8 to detach from the lead wire 6, thus reliablydisconnecting the current. Then, part of the metal foil 2 correspondingto the crescent-like slit 3 bursts to form the valve opening portion 7so that the internal pressure is released outside. The gas generatedfrom the electrolyte passes through the valve opening portion 7 and isdischarged from the through holes 0 of the closing cap 33. Asillustrated in FIG. 5 for explaining the operating manner of the valvechip V, once any case needs the valve chip to operate, it permits thevalve opening portion 7 to be formed to thereby release the internal gasof the battery. Thus, the battery can previously be prevented from theabrupt rising of the internal temperature or explosion thereof. Theoperating pressure for the valve chip can be controlled by manufacturingthe metal foil with the highest accuracy of its thickness in micronorder. Further, the operating pressure can be predetermined within astable pressure range by selecting the material composition of the valvechip and adjusting the length of the bending fulcrum portion 4.

EFFECT OF THE INVENTION

According to the safety valve chip of the present invention, when theinternal pressure of a battery is elevated due to short circuit,overcharge, reverse charge, or the like, and at the time when it reachesto a prescribed pressure, the valve element can smoothly be raised upand the metal foil is allowed to burst stably and accurately even at alow pressure so as to release the internal gas of the battery. Thus, thebattery can previously be prevented from the abrupt rising of thetemperature or explosion thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical section view showing an upper part of thecompletely closed battery according to the present invention.

FIG. 2 is a plane view showing the valve chip according to the presentinvention.

FIG. 3 is a section view taken along Y—Y in FIG. 2.

FIG. 4 is an explanatory view showing the operating manner of the valvechip in case of abnormality.

FIG. 5 is another explanatory view showing the operating manner of thevalve chip in case of abnormality.

FIG. 6 is a plane view showing another embodiment of the valve chipaccording to the present invention.

EXPLANATION OF REFERENCE CHARACTERS

1: metal substrate

2: metal foil

3: slit

4: bending fulcrum portion

5: valve element

6: lead wire

7: valve opening portion

8: braze portion

Cl : center of valve element

C2 :center of valve opening portion

What is claimed is:
 1. A closed battery comprising: an electrode elementconsisting of a positive electrode, a negative electrode, and aseparator; an electrolyte; a battery container accommodating saidelectrode element together with said electrolyte; and a closing memberfitted in the inner periphery of an open end portion of said batterycontainer to close the open end portion of the battery container,wherein said closing member consists of a metal substrate, a valveelement which is provided in said metal substrate with a slit so as toserve as a releasing chip such that when the internal pressure of thebattery is elevated, the valve element is bent from a bending fulcrum soas to provide the metal substrate with an opening portion for releasingthe internal pressure, and a metal foil which is adhered to the innersurface of the metal substrate, wherein said valve element is providedwith a slit between the circumference thereof and said metal substrate,and the center of said valve element is eccentric to the center of saidmetal substrate.
 2. A closed battery according to claim 1, wherein saidmetal foil is connected with a lead member for conducting a current fromthe electrode element to a closing cap, and when said valve elementoperates to release the internal pressure, said lead member iselectrically disconnected from the metal foil to break the current.
 3. Aclosed battery according to claim 1, wherein said valve element has asubstantially circular form and is provided around the circumferencethereof with a slit whose width is positionally varied, and said valveelement is provided with a part serving as a bending fulcrum portion. 4.A closed battery according to claim 3, wherein said valve element has asubstantially circular form and is provided around the circumferencethereof with a slit whose width is positionally varied, and the bendingfulcrum is provided with an arm portion.
 5. A closed battery accordingto claim 1, wherein said metal substrate is made of any one selectedfrom the group including a steel sheet, stainless steel sheet, coppersheet, and aluminum sheet.
 6. A closed battery according to claim 1,wherein said metal foil is any one selected from the group including asteel foil, stainless steel foil, copper foil, aluminum foil, nickelfoil, and nickel-iron alloy foil.
 7. A closing member incorporated intoa closed battery according to claim 1.